A large number of porous filament filter bags are produced by a process commonly known as "melt-blowing." In this process, micro-woven filaments are melted and propelled toward a target surface, usually a rotating drum where the material is formed into a laminated layer. This process is described in U.S. Pat. Nos. 3,972,759 and 3,978,185. After the layer is collected from about the rotating drum, it is cut into pieces which are approximately the size of a filter bag and each piece when is stitched together to form a continuous wall for the bag. Such stitching lowers the efficiency of the filter bag around the needle holes and increases the possibilities of bag separation under high operating pressures.